For the cheap bar sander, no need to be Norm Abrahms

Get get a piece of hardwood about 2-3 inches wide and 24 or so inches long. (If you go to home depot or a store like that, check out hardwood flooring, pre laminated. Lots of times the tongue or grooves on a piece are damaged and useless for flooring. Doesn't hurt to ask for it or at least pay a $1-2 cost)

Double sided tape at Walmart, $2 for 50 feet. Also get a roll of sandpaper $4 for 25 foot roll. You won't use the full width; probably half. Use the laminated side to tape the sandpaper to; and it's easy to remove but holds until you want it off.

voila, a cheap sanding bar with no woodworking.

Bob